Wrangellia Terrane

The Wrangellia Terrane (named for the Wrangell Mountains, Alaska) is a terrane extending from the south-central part of Alaska through southwestern Yukon and along the Coast of British Columbia in Canada. Some geologists contend that Wrangellia extends southward to Oregon,[1] although this is not generally accepted.

Current location and extent of Wrangellia

Extent and terminology

The term Wrangellia is confusingly applied to all of:

  • The Wrangell(ia) Terrane alone;
  • A composite terrane (CT) consisting of the Wrangell Terrane, Peninsular Terrane, and other rock units that were not originally part of the North American craton;
  • A composite terrane which also includes the Alexander Terrane.

Earlier geologists sometimes used the term "Talkeetna Superterrane" to describe Wrangellia.[2]

Origin

There are two conflicting hypotheses whether the Wrangellia Superterrane originated at polar or equatorial latitudes:

  1. That Wrangellia accreted at a northerly latitude near its current location (when North America, or Laurentia, was farther east as part of Pangaea).
  2. That it originated c. 3,000 km (1,900 mi) south of its current location, approximately where Baja California is now. This hypothesis is not favoured in most plate tectonic reconstructions, since it introduces rapid implausible displacements of Wrangellia across the Panthalassic Ocean.[3]

Southern hypothesis

Rocks of Wrangellia (the individual terrane, not the composite terrane) were originally created in the Pennsylvanian to the Jurassic somewhere, but probably near the equator, in the Panthalassic Ocean off the west coast of the North American craton as island arcs, oceanic plateaus, and rock assemblages of the associated tectonic settings. It is composed of many rocks types, of various composition, age, and tectonic affinity, but the Late Triassic flood basalts are the defining unit of Wrangellia. These basalts, extruded onto land over 5 million years about 230 million years ago, on top of an extinct Pennsylvanian and Permian island arc, constitute a large igneous province, currently exposed in a 2,500 km (1,553 mi) long belt.[4]

Wrangellia collided and amalgamated with the Alexander Terrane by Pennsylvanian time. By the end of the Triassic, the Peninsular Terrane had also joined the Wrangellia composite terrane. A subduction zone existed on the west side of Wrangellia. Seafloor rocks too light to be subducted were compressed against the west edge of Wrangellia; these rocks are now known as the Chugach Terrane. A complex fault system, known as the Border Ranges Fault, is the modern expression of the suture zone between Wrangellia and Chugach Terranes. Over time, plate tectonics moved this amalgamation of crust generally northeastward into contact with the North American continental margin. The Wrangellia composite terrane collided with and docked to North America by Cretaceous time. Strike-slip displacement, with Wrangellia travelling northward, continued after docking, although the amount of post-accretion displacement is controversial.[5]

Northern hypothesis

Geological evidences indicate that the Caledonide closure of the Iapetus and Rheic oceans along the Laurentian westcoast (modern coordinates) also opened an ocean between the northern margin of Laurentia and Baltica on one side and Siberia on the other. This effectively dispersed continental fragments—the Alexander, Eastern Klamath, Northern Sierra and Okanagan terranes—westward along the shores of this ocean in a back-arc process similar to that of the present-day Scotia Plate between South America and Antarctica. During the Carboniferous, the Alexander terrane migrated westward into the northern Panthalassa Ocean where it merged with Wrangellia in the late Carboniferous—the two continental fragments remained isolated in the open ocean until they were accreted to Laurentia in the Middle Jurassic.[6]

See also

References

Citations
  1. Sarewitz 1983, Abstract
  2. Wallace, Hanks & Rogers 1989, Abstract
  3. Nokleberg et al. 1998, Paleomagnetic Dilemma: Loci of Accretion of Wrangellia Superterrane, pp. 9–10
  4. Rogers & Schmidt 2002, Abstract; Greene et al. 2004, Introduction, p. 10
  5. Nokleberg, Jones & Silberling 1985, Abstract; Trop et al. 2002, Abstract; Israel 2009, Abstract; Greene, Scoates & Weis 2005, p. 211
  6. Colpron & Nelson 2009, Geodynamic model, pp. 295–299

General sources
  • Colpron, M.; Nelson, J. L. (2009). "A Palaeozoic Northwest Passage: Incursion of Caledonian, Baltican and Siberian terranes into eastern Panthalassa, and the early evolution of the North American Cordillera". Geological Society, London, Special Publications. 318 (1): 273–307. doi:10.1144/SP318.10. Retrieved 23 December 2019.CS1 maint: ref=harv (link)
  • Greene, A. R.; Scoates, J. S.; Weis, D. (2005). "Wrangellia Terrane on Vancouver Island, British Columbia: Distribution of Flood Basalts with Implications for Potential Ni-Cu-PGE Mineralization in Southwestern British Columbia" (PDF). Geological Fieldwork 2004. British Columbia Geological Survey. pp. 209–220. Retrieved 3 December 2007.CS1 maint: ref=harv (link)
  • Greene, A. R.; Scoates, J. S.; Weis, D.; Israel, S. (2005). "Flood basalts of the Wrangellia Terrane, southwest Yukon: Implications for the formation of oceanic plateaus, continental crust and Ni-Cu-PGE mineralization" (PDF). In Emond, D. S.; Lewis, L. L.; Bradshaw, G. D. (eds.). Yukon Exploration and Geology 2004. Yukon Geological Survey. pp. 109–120. Retrieved 30 April 2018.CS1 maint: ref=harv (link)
  • Israel, S. A. (2009). Stratigraphic and Tectonic Relationships of the Paleozoic Portion of Wrangellia. Cordilleran Section Meeting - 105th Annual Meeting.CS1 maint: ref=harv (link)
  • Nokleberg, W. J.; Jones, D. L.; Silberling, N. J. (1985). "Origin and tectonic evolution of the Maclaren and Wrangellia terranes, eastern Alaska Range, Alaska". Geological Society of America Bulletin. 96 (10): 1251–1270. doi:10.1130/0016-7606(1985)96<1251:OATEOT>2.0.CO;2.CS1 maint: ref=harv (link)
  • Nokleberg, W. J.; Parfenov, L. M.; Monger, J. W. H.; Norton, I. O.; Khanchuk, A. I.; Stone, D. B.; Scholl, D. W.; Fujita, K. (1998). Phanerozoic tectonic evolution of the Circum-North Pacific (PDF) (Report). USGS Open-file report 98-754. Retrieved 30 April 2018.CS1 maint: ref=harv (link)
  • Rogers, R. K.; Schmidt, J. M. (2002). Metallogeny of the Wrangellia terrane in the Talkeetna Mountains, southern Alaska. Geological Society of America Abstracts with Programs. 34. p. 101. Retrieved 30 April 2018.CS1 maint: ref=harv (link)
  • Sarewitz, D. (1983). "Seven Devils terrane: Is it really a piece of Wrangellia?". Geology. 11 (11): 634–637. doi:10.1130/0091-7613(1983)11<634:SDTIIR>2.0.CO;2.CS1 maint: ref=harv (link)
  • Trop, J. M.; Ridgway, K. D.; Manuszak, J. D.; Layer, P. (2002). "Mesozoic sedimentary-basin development on the allochthonous Wrangellia composite terrane, Wrangell Mountains basin, Alaska: A long-term record of terrane migration and arc construction". Geological Society of America Bulletin. 114 (6): 693–717. doi:10.1130/0016-7606(2002)114<0693:MSBDOT>2.0.CO;2.CS1 maint: ref=harv (link)
  • Wallace, W. K.; Hanks, C. L.; Rogers, J. F. (1989). "The southern Kahiltna terrane: Implications for the tectonic evolution of southwestern Alaska". Geological Society of America Bulletin. 101 (11): 1389–1407. doi:10.1130/0016-7606(1989)101<1389:TSKTIF>2.3.CO;2.CS1 maint: ref=harv (link)
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